1. Field of the Invention
The present invention relates to an apparatus for forming a thin film, and more particularly, to an apparatus for forming a thin film, belonging to a plasma chemical vapor deposition device, which delimits a glow discharge space by a plasma carrier to thereby simplify a cleansing procedure and enhance productivity while affording advantages of a box carrier type plasma chemical vapor deposition device.
2. Description of the Prior Art
Generally, since a plasma chemical vapor deposition device carries out almost all of its processes at a relatively low temperature and can produce a uniform thin film over a large area, it is widely used in fabricating or forming a semiconductor or an insulating layer which is needed for manufacturing a semiconductor integrated circuit, a thin film transistor liquid crystal display (TFT LCD), a solar cell, etc.
As a plasma chemical vapor deposition device suitable for mass production, several devices of various types including box carrier type, roll-to-roll type, in-line type and plasma box type have been developed. Among these devices, the box carrier type plasma chemical vapor deposition device is advantageous in an economical viewpoint as compared to the others in that it is inexpensive, it has a high productivity due to its processing of parts by a batch unit, and the utilization efficiency of a plasma gas is elevated.
Referring to FIG. 1, there is illustrated a cross-sectional view of an apparatus for forming a thin film, of the prior art.
A box carrier 10 of the apparatus for forming a thin film, of the prior art, has a glow discharge space 14 delimited by a radio frequency (RF) electrode 11 and ground electrodes 12 and 13, a plasma gas intake space 15 for supplying a plasma gas into the glow discharge space 14, and a reaction gas exhaust space 16 for ejecting a reaction gas from the glow discharge space 14.
Four substrates 17 on each of which a thin film is to be grown are mounted against both surfaces of the RF electrode 11 and inner surfaces of the ground electrodes 12 and 13, respectively, in a state that the ground electrodes 12 and 13 are moved to an open position. After the substrates 17 are mounted as described above, the ground electrodes 12 and 13 are moved to a closed position, and the box carrier 10 is pushed into a reaction chamber (not shown).
The reaction chamber is maintained at a constant temperature and under a constant pressure, and the plasma gas and RF power are supplied to the box carrier 10.
For example, in case of a solar cell, p, i and n layers made of amorphous silicon are continuously grown. SiH.sub.4 is mainly used as the plasma gas for a thin film made of amorphous silicon, and B.sub.2 H.sub.6 and PH.sub.3 are added as doping gases when forming the p layer and the n layer, respectively.
By applying an RF power of 13.56 MHZ to the RF electrode 11 while supplying the plasma gas into the box carrier 10, glow discharge occurs in the glow discharge space 14, and according to this, a thin film is grown on an inner surface of the box carrier 10 facing the glow discharge space 14 and on inner surfaces of the substrates 17. After the reaction is completed, the box carrier 10 is drawn out of the reaction chamber, the ground electrodes 12 and 13 are moved again to the open position, and the substrates 17 are taken out.
At this time, the thin film coated onto the inner surface of the box carrier 10 is peeled off, floated in the reaction chamber in the form of particles and adhered to substrates 17 onto which thin films are to be newly formed, thereby causing flaws in the substrates 17. For this reason, the used box carrier 10 is disassembled and cleansed. An a-Si thin film coated onto the inner surface of the box carrier 10 is removed by impregnating the box carrier 10 with alkaline solution such as KOH for a lengthy period of time. The box carrier 10 stained with the alkaline solution is cleaned by deionized water. After removing the deionized water from the inner surface of the box carrier 10 by employing dried air or nitrogen, the box carrier 10 is completely dried in a drying furnace.
However, the apparatus for forming a thin film of the prior art, constructed as mentioned above, suffers from defects in that a great deal of time and human effort are required for disassembling and cleansing the box carrier, it costs a great deal to prepare utilities such as deionized water, nitrogen, electric power, etc. and treat the alkaline solution. Also, while it is economical to pursue mass production to reduce the price of an end product, and a typical way to enhance productivity of a plasma chemical vapor deposition procedure is to enlarge an area of a substrate and automate various processes, the box carrier of the plasma chemical vapor deposition device of the prior art is greatly involved in mounting/dismounting the substrates, loading the box carrier and disassembling/cleansing/assembling the box carrier, so that it is not suited for mass production. Further, in case of enlarging the area of the substrate, the electrodes constituting a main portion of the box carrier must readily conduct electric current and must not be corroded while being cleansed with the alkaline solution, for which reason the electrodes are made of stainless steel, an area of the electrode must be larger than the area of the substrate to obtain a uniform thin film over the entire substrate, and a distance between the electrodes must be kept constant. Accordingly, as the area of the substrate is enlarged, since the area of the electrode is also enlarged and a thickness thereof must also be increased to prevent deformation due to heat or outside shock, the more the area of the substrate is enlarged, the more the size and weight of the box carrier are increased, whereby it is more difficult to properly handle the box carrier.